7.0 Overview
If the universe was born from a big explosion called “the big bang” then it is expanding and the
distances between galaxies is growing. This does not mean there is an edge to the universe —
space could continue on infinitely in all directions but there could be a horizon beyond which
there is no content.
There can be an observable edge to the universe, but it is more of a horizon, just as there is a
horizon to the ocean, we know beyond the horizon there is more water. Since the universe was
born 13.82 billion years ago in the Big Bang we can only see those galaxies whose light has taken
less than 13.82 billion years to reach us. These galaxies form a sphere around the Earth called
“the observable universe”. It is 92 billion light years in diameter because in its beginning the
universe inflated much faster than the speed of light.
The Schwartzchild radius:
Gives the event horizon of a black hole. I have heard it said if the mass, M, is the mass of the
universe, that radius is the edge of the observable universe that, the observable edge of the
universe is actually the event horizon of a black hole and that then the Universe is a giant black
hole and that we are inside of it. I would like to call this to question, but first let’s discuss the
types of possible universes.
The pivotal parameter describing the universe is 𝛀 (omega) which is the average matter density
of the universe divided by a critical value of that density. Whether omega is less than1, 1, or
greater than 1 determines whether the Universe is open, flat, or closed. If matter is mostly inert
as in the dust models, there is a particular fate for each omega. Since 1998 the observations in
supernovas indicate the universe is accelerating in its expansion. To explain this cosmologists
hypothesize the existence of dark energy which can be any field with negative entropy causing
negative pressure. If 𝛀<1 then the Universe is open and the fate of the universe is in its heat
death, the burning out of the last stars born. This is also true of a flat universe if it has the
hypothesized dark energy, because then it accelerates to escape collapse. The fate of the universe
depends on its density and today most evidence points to it will expand indefinitely. In this
scenario there is enough a supply of gas for stars to form for 10¹² to 10¹⁴ years. 1 to 100 trillion
years. That is the last stars born would die in 10¹⁴ years. There are models that suggest the
universe is eternal where as stars die more matter comes into existence from which more stars
are continuously forming.
Now let’s call into question that the edge of the observable universe is the Schwartzchild radius,
the event horizon of a blackhole.
I had seen a documentary where they said there was a cosmologist working on a theory that the
edge of the observable universe is the event horizon of a blackhole. I thought okay as weird as
that seems, and I say weird because that means either the Earth is at the center of this blackhole,
or if not, mysteriously wherever you are in the universe is the center. I accepted this as possible
because the more we learn the stranger the universe gets. Indeed a long time ago Niels Bohr said
that if you haven’t realized that quantum mechanics says everything that makes up the universe
can’t be considered real, you have missed its point. And indeed if you think about quantum
mechanics, this rings true, so yes I was able to accept this about the edge of the universe, as